FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art. Wireless telecommunications system 100 comprises: wireless terminal 101, cellular base stations 102-1, 102-2, and 102-3, Wi-Fi base stations 103-1 and 103-2, wireless switching center 111, assistance server 112, location client 113, and Global Positioning System (“GPS”) constellation 121. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
The salient advantage of wireless telecommunications over wireline telecommunications is the mobility that is afforded to the user of the wireless terminal. On the other hand, the salient disadvantage of wireless telecommunications lies in that fact that because the wireless terminal is mobile, an interested party might not be able to readily ascertain the location of the wireless terminal.
Such interested parties might include both the user of the wireless terminal and remote parties. There are a variety of reasons why the user of a wireless terminal might be interested in knowing his or her location. For example, the user might be interested in telling a remote party where he or she is or the user might seek advice in navigation.
In addition, there are a variety of reasons why a remote party might be interested in knowing the location of the user. For example, the recipient of an 9-1-1 emergency call from a user might be interested in knowing the location of the wireless terminal so that emergency services vehicles can be dispatched to the user.
There are many techniques in the prior art for estimating the location of a wireless terminal. The common theme to these techniques is that location of the wireless terminal is estimated based on the electromagnetic (e.g., radio, etc.) signals—in one form or another—that are processed (i.e., transmitted or received) by the wireless terminal.
In accordance with one family of techniques, the location of a wireless terminal is estimated based on the transmission range of the base stations with which it is communicating. Because the range of a base station is known to be N meters, this family of techniques provides an estimate for the location that is generally accurate to within N meters. A common name for this family of techniques is “cell identification” or “cell ID.”
There are numerous tricks that can be made to the basic cell ID technique to improve the accuracy of the estimate for the location, and numerous companies like Ericsson, Qualcomm, and Google each tout their own flavor. The principal disadvantage of the family of cell ID techniques is that there are many applications for which the accuracy of the estimate for the location it generates is insufficient.
In accordance with a second family of techniques, the location of a wireless terminal is estimated by analyzing the angle of arrival or time of arrival of the signals transmitted by the wireless terminal. A common, if somewhat inaccurate, name for this family of techniques is called “triangulation.”
There are numerous tricks that can be made to the basic triangulation technique to improve the accuracy of the estimate for the location, and numerous companies like TruePosition each tout their own flavor. The principal disadvantage of the triangulation techniques is that there are many applications for which the accuracy of the estimate for the location it generates is insufficient.
In accordance with a third family of techniques, the location of a wireless terminal is estimated by a receiver in the wireless terminal that receives signals from satellites in orbit. A common name for this family of techniques is “GPS.”
There are numerous tricks that can be made to the basic GPS technique to improve the accuracy of the estimate for the location, and numerous companies like Qualcomm each tout their own flavor. The principal advantage of the GPS techniques is that when it works, the estimate for the location can be accurate to within meters. The GPS techniques are disadvantageous in that they do not work consistently well indoors, in heavily-wooded forests, or in urban canyons.
In accordance with a fourth family of techniques, the location of a wireless terminal is estimated by pattern matching one or more location-dependent traits of one or more electromagnetic signals that are processed (i.e., transmitted and/or received) by the wireless terminal. Common names for this family of techniques include “Wireless Location Signatures,” “RF Pattern Matching,” and “RF Fingerprinting.”
The basic idea is that some traits of an electromagnetic signal remain (more or less) constant as a signal travels from a transmitter to a receiver (e.g., frequency, etc.) and some traits change (e.g., signal strength, relative multi-path component magnitude, propagation delay, etc.). A trait that changes is considered a “location-dependent” trait. Each location can be described or associated with a profile of one or more location-dependent traits of one or more electromagnetic signals. A wireless terminal at an unknown location can observe the traits and then attempt to ascertain its location by comparing the observed traits with a database that correlates locations with expected or predicted traits.
There are numerous tricks that can be made to the basic Wireless Location Signatures technique to improve the accuracy of the estimate for the location, and numerous companies like Polaris Wireless each tout their own flavor. The principal advantage of the Wireless Location Signatures technique is that it is highly accurate and works well indoors, in heavily-wooded forests, and in urban canyons.
All of these techniques rely on empirical data as their basis, and the accuracy of these techniques suffer when some or all of the data is misleading or erroneous. Typically, it is easy to identify and disregard data that is clearly unreasonable. For example, if one datum indicates that a wireless terminal is inside of the Sun, that datum is clearly erroneous and can be disregarded. In some cases a reasonable estimate for the location of the wireless terminal can be generated with the remaining data, and sometimes it cannot.
In contrast, it is difficult to identify data that is apparently reasonable, but misleading or erroneous. For example, if one datum in a set of data suggests a wireless terminal is on a lake near a highway, the datum appears reasonable, but it might or might not be erroneous. For example, the datum might be entirely correct because the wireless terminal is on a boat on the lake. Alternatively, the datum might be erroneous because the wireless terminal is in a car on the highway next to the lake. In either case, it is not easy to know whether using that datum is improving or degrading the overall accuracy of the estimate.
Unfortunately, apparently reasonable, but erroneous or misleading empirical data is commonly used as the basis for estimating the location of a wireless terminal, and, therefore, a technique is needed that ameliorates or eliminates the effect of such data.